The invention relates generally to the field of motor vehicle brake systems. Specifically, an electrohydraulic motor vehicle brake system having an electromechanical actuator for actuating the brake system is described.
Electromechanical actuators have already been in use for some time in motor vehicle brake systems, for example to produce an electric park brake function (EPB). In electromechanical brake systems (EMB), they replace the conventional hydraulic cylinders at the wheel brakes.
Because of technical progress, the efficiency of electromechanical actuators has increased continuously. Consideration has therefore been given to the use of such actuators also for implementing modern vehicle dynamics control systems. Such control systems include an anti-lock braking system (ABS), a traction control system (TCS) or an electronic stability program (ESP), also known as vehicle stability control (VSC).
WO 2006/111393 A teaches an electrohydraulic brake system having a highly dynamic electromechanical actuator which performs pressure modulation during electronic stability control operation. The electromechanical actuator described in WO 2006/111393 A is provided to act directly on a master cylinder of the brake system. Because of the high dynamics of the electromechanical actuator, the hydraulic components of the brake system known from WO 2006/111393 A can be reduced to a single 2/2-way valve per wheel brake. In order to carry out pressure modulations at individual wheels, the valves are then activated individually or in groups in multiplex operation.
However, the minimisation to merely one valve per wheel brake also results in challenges, such as an undesired pressure equalisation when the valves are open at the same time. A solution based on a highly dynamic control behaviour therefor is provided in WO 2010/091883 A.
WO 2010/091883 A discloses an electrohydraulic brake system having a main cylinder and a tandem piston accommodated therein. The tandem piston can be actuated by means of an electromechanical actuator. The electromechanical actuator comprises an electric motor arranged concentrically with the tandem piston, and a gear arrangement which converts a rotational movement of the electric motor into a translational movement of the piston. The gear arrangement consists of a ball screw having a ball screw nut, which is coupled in a rotationally secure manner to a rotor of the electric motor, and a ball screw shaft, which acts on the tandem piston.
A further electrohydraulic brake system having an electromechanical actuator which acts on a master cylinder piston is known from WO 2012/152352 A. This system is able to work in a regenerative mode (generator operation).